1. The Field of the Invention
The present invention relates generally to an improvement in the ability of test systems to measure a signal propagation delay through objects (e.g., devices and/or cables used to connect these devices).
2. The Relevant Technology
A bit error rate (“BER”) is a ratio of bits received, processed, and/or transmitted with errors to a total number of bits received, processed, and/or transmitted over a given period of time. If, for example, a transmission has 1 million bits and one of these bits is in error (e.g., a bit is in a first logic state instead of a second logic state), the transmission has a BER of 10−6. The BER is useful because it can be used to characterize the ability of a device to receive, process, and/or transmit bits.
Many devices are designed to receive, process, and then transmit a plurality of bits. An optoelectronic transceiver, for example, typically receives a plurality of bits in an electrical form and then transforms and transmits the bits in an optical form and/or receives a plurality of bits in an optical form and then transforms and transmits the bits in an electrical form. Such devices require a finite amount of time to make these transformations. This finite amount of time is known as the signal propagation delay. It is often useful to measure the signal propagation delay for a particular signal traveling from one point to another. The points can be relatively close, such as two devices on the same local area network, or widely scattered, such as two devices in different cities. Measuring the signal propagation delay enables individuals to identify whether or not data propagates efficiently between the two points.
In the past, measuring a propagation delay through a device and/or cables used to connect these devices was a costly operation that included expensive equipment such as an Agilent or Anritsu Signal Generator or the Agilent or Tektronix Digital Communication Analyzer. In order to use this prior art device, one needed a signal generator, a signal splitter, the device under test (DUT), and an oscilloscope with two channels. One would then need to connect the output of the signal generator through the signal splitter to the DUT input and the first channel of the oscilloscope. The second channel of the oscilloscope could then be connected to the DUT output. Then, using either the oscilloscope screen or the screen file of the analyzer, one could figure out the propagation delay, which would then correspond to a time distance between two wave forms. Using this method, scopes with a precise time base give better resolution. Unfortunately, one needs a very large memory capacity to measure long delays in a precise time base with high resolution.